1. Field of the Invention
The present invention is concerned with new anti-reflective compositions for use in the manufacture of microelectronic devices. These compositions include little or no strong acids so that premature crosslinking (e.g., such as during storage) is minimized or prevented.
2. Description of the Prior Art
Integrated circuit manufacturers are consistently seeking to maximize substrate wafer sizes and minimize device feature dimensions in order to improve yield, reduce unit case, and increase on-chip computing power. Device feature sizes on silicon or other chips are now submicron in size with the advent of advanced deep ultraviolet (DUV) and i-line microlithographic processes.
However, a frequent problem encountered by photoresists during the manufacturing of semiconductor devices is that activating radiation is reflected back into the photoresist by the substrate on which it is supported. Such reflectivity tends to cause blurred patterns which degrade the resolution of the photoresist. Degradation of the image in the processed photoresist is particularly problematic when the substrate is highly reflective. One approach to address this problem is the use of an anti-reflective coating applied to the substrate beneath the photoresist layer.
One problem encountered with many prior art anti-reflective coating formulations is that they commonly use a thermal crosslinking system to yield a polymer-containing film which is insoluble in common photoresist solvents. Crosslinking of the anti-reflective coating should only occur during the wafer bake stage, which is usually very short (e.g., 30-90 seconds). However, to generate a crosslinking reaction during such a short bake period, a strong acid catalyst such as p-toluenesulfonic acid has been required. The use of such strong acid catalysts in an anti-reflective coating formulation creates processing problems. That is, a strong acid catalyst not only enables anti-reflective coating crosslinking during the wafer bake stage, but also while the anti-reflective coating material is still in the spin bowl or drain pipes. This crosslinked anti-reflective coating will no longer dissolve in conventional cleaning solvents, thus, the anti-reflective coating material remains and accumulates in the spin bowl and drain pipes. This problem is known as spin bowl incompatibility.
Since spin coating has long been the industry accepted method of coating anti-reflective coatings and photoresists onto wafers, spin bowl incompatibility causes significant process interruptions and down time for wafer processing facilities. Accumulation of the crosslinked anti-reflective coating and precipitation thereof in photoresist solvents can block the spinner drain pipes. This prevents waste material flow and may result in a small pool of waste photoresist collecting in the bottom of the spinner. Since the crosslinked anti-reflective coating cannot be dissolved with solvents, the spinner must be disassembled to clear the drain, thus adding additional time and expense to the process.
Spin bowl incompatibility also causes the crosslinked anti-reflective coating to deposit on the sides of the spin bowl. This “build-up” prevents waste material from flowing smoothly down the sides of the spin bowl and into the drain. Eventually such build-up will be sufficiently present that it will interfere with wafer processing. Again, because the crosslinked anti-reflective coating material cannot be cleaned with solvents, it may be necessary to replace the contaminated spin bowl with a new one. It will be appreciated that this is both time-consuming and costly. Furthermore, because most wafer processing facilities use automated, track-type systems, replacing spin bowls and cleaning drain pipes stop the track and results in downtime for an entire processing operation.
There is a need for new anti-reflective coatings which are spin bowl compatible and have improved stability at room temperature while simultaneously exhibiting the desired performance characteristics of DUV, and i-line, and 193 nm anti-reflective coating materials.